Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be otherwise possible to do so. Artificial joints are usually comprised of metal, ceramic and/or plastic components that are fixed to existing bone.
Such joint replacement surgery is otherwise known as joint arthroplasty. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto.
There are known to exist many designs and methods for manufacturing implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints such as elbows, hips, knees and shoulders.
Currently in total hip arthroplasty, a major critical concern is the instability of the joint. Instability is associated with dislocation. Dislocation is particularly a problem in total hip arthroplasty.
Factors related to dislocation include surgical technique, implant design, implant positioning and patient related factors. In total hip arthroplasty, implant systems address this concern by offering a series of products with a range of lateral offsets, neck offsets, head offsets and leg lengths. The combination of these four factors affects the laxity of the soft tissue. By optimizing the biomechanics, the surgeon can provide a patient a stable hip much more resistant to dislocation. In order to accommodate the range of patient arthropometrics, a wide range of hip implant geometries are currently manufactured by DePuy Orthopaedics, Inc., the assignee of the current application, and by other companies. In particular, the S-ROM® total hip systems offered by DePuy Orthopaedics, Inc. include three offsets, three neck lengths, four head lengths and one leg length adjustment. The combination of all these biomechanic options is rather complex.
Anteversion of a total hip system is closely linked to the stability of the joint. Improper version can lead to dislocation and patient dissatisfaction. Version control is important in all hip stems. However, it is a more challenging issue with the advent of stems with additional modularity.
The prior art has provided for some addressing of the anteversion problem. For example, the current S-ROM® stems have laser markings on the medial stem and the proximal sleeve. This marking enables the surgeon to measure relative alignment between these components. Since the sleeve has infinite anteversion, it is not necessarily oriented relative to a bony landmark that can be used to define anteversion. In fact, the current sleeves are sometimes oriented with the spout pointing directly laterally into the remaining available bone.
Prior art stems may be aligned relative to a patient's bony landmarks. These stems are monolithic. They cannot locate the neck independently of the distal stem. Therefore, anteversion is limited. Most bowed, monolithic stems are sold in fixed anteversion; for example, at an anteversion of 15 degrees. These monolithic stems have limited flexibility for rotational alignment since the distal stem must follow the bow of the patient's femur and this may not provide an operable biomechanical result.
In a common step in the surgical procedure known as total hip arthroplasty, a trial or substitute stem is first implanted into the patient. The trial is utilized to verify the selected size and shape of the implant in situ on the patient and the patient is subjected to what is known as a trial reduction. This trial reduction represents moving the joint, including the trial implant through selected typical motions for that joint. Current hip instruments provide a series of trials of different sizes to help the surgeon assess the fit and position of the implant. Trials, which are also known as provisionals, allow the surgeon to perform a trial reduction to assess the suitability of the implant and implant's stability prior to final implant selection.
Most hip stems implanted currently are of a one-piece or mono-block design. Mono-block hip stem designs allow for no adjustments. Thus, they require that the hip stem be removed and replaced to adjust head height or offset. Also, mono-block stems are not designed to be used in minimally invasive surgery and are not optimal for use with minimally invasive surgery procedures.
Surgical variables such as leg length discrepancy may result in surgical error that may need to be corrected or optimized. Further, due to implant subsidence during the use of an implant, the head-height at a revision surgery may need to be corrected. Further, revision surgery may be required to correct the instability of the hip joint. Stability may be restored by moving the head proximally and or increasing the offset of the implant to tighten the soft tissues. These corrections may be made at revision surgery to address these dislocations, however with current mono-block stems the stem must be removed from the femur to accomplish these changes in the implant configuration. Such removal of the stem from the femur may make the revision surgery quite difficult in that the stem tends to engrow with the tissues of the bone. Also, removal of the stem may lead to significant loss of bone, which can compromise the fixation of the stem upon re-implantation.
Further revision surgery may be required to correct weak abductor function by increasing the offset of the stem. The changing in a revision surgery to an increased offset stem may require that the stem be removed from the medullary canal of the femur and replaced with a stem with a different offset.
Further mono-block stems are not easily used in minimally invasive hip procedures where the incision through the skin and soft tissue is minimized. The surgeon may have difficulty to work in the joint space after the stem is in place. The neck of the mono-block stem may be in the way during the performance of the surgery.
In order to reduce inventory costs and complexity, many trialing systems are modular. For example, in the Excel Instrument System, a product of DePuy Orthopaedics, Inc., there is a series of broaches and neck trials that can be mixed and matched to represent the full range of implants. There is a single fixed relationship between a broach and a neck trial, because these trials represent a system of monolithic stem implants.
Likewise, in the current S-ROM® instrument systems provided by DePuy Orthopaedics, Inc., there are neck, proximal body, distal stem, head and sleeve trials. By combining all these components, the implant is represented. Since the S-ROM® stem is modular and includes a stem and a sleeve, the angular relationship or relative anteversion between the neck and the sleeve is independent and represented by teeth mating between the neck and the proximal body trial. The proximal body trial has fixed transverse bolts that are keyed to the sleeve in the trialing for straight, primary stems. The long stem trials do not have the transverse bolts and are thus not rotationally stable during trial reduction and therefore are not always used by the surgeon.
Prosthetic joint implants are currently surging in use and technology. In performing most prosthetic joint implants, what is known as a ‘trial’ or ‘provisional’ is used before a final prosthesis is used. The trial or provisional is used to select the proper joint prosthesis and/or to orient or align one or more of the components of the final joint prosthesis. The trial or trial components are temporarily implanted to achieve proper sizing, placement and/or orientation of the final joint prosthesis, as well as achieve anatomical orientation of the prosthesis and/or components of the joint prosthesis.
Hip arthroplasty provisionals or trials have a neck that is used to attach a femoral head provisional or trial thereto. The orientation of the neck relative to the shaft of the broach or trial is described in terms of anteversion, neck length, neck angle, and/or neck offset. Because each patient's original femoral neck anatomy is different, the ability to replicate the original femoral neck anatomy of each patient during hip arthroplasty requires multiple neck trials having various orientations. The use of multiple neck segments is not advantageous since it requires more time, increased instrument cost and increased space in the instrument sterilization case.
Thus, trialing systems utilized by many hip implants or prostheses generally consist of a broach and a neck segment. In order to intraoperatively change the offset of the trial (i.e. neck segment and broach), the neck trial must be removed and another neck trial must be put in its place. Thus, multiple neck trials that are exchangeable with one another relative to the broach are necessary in order to replicate the original hip anatomy.
Other hip systems utilize only one neck segment with the offset incorporated into the location of the trunnion of the broach. This design, however, does not mimic the exact geometry of the actual implant. While it is desired to be able to try several neck offsets relative to the broach in order to achieve a proper head positioning for the final implant, the prior art is deficient.
In U.S. Pat. No. 5,645,607 issued to Hickey, a hip trial or prosthesis having an adjustable neck portion is disclosed in which the problem of multiple neck trials is addressed. The adjustable neck of Hickey allows the trialing of various neck offsets in order to achieve a correspondence between the spatial orientation of a patient's original anatomy and a final implanted hip ball prosthesis.
However, Hickey requires a vertical height change of the neck segment in order to move between the various offsets. Where vertical height is restricted during surgery, especially in current, less invasive arthroplasty procedures, vertical height adjustment is undesirable.
There are a variety of modular stem designs in the prior art. Most of these designs focus on the ability to use varying stem diameters and length with various size proximal bodies to provide optimal fill on both the diaphysis and the metaphysis simultaneously (to optimize fixation of the device). In many of these designs the neck cannot be removed or replaced to adjust head-height or offset without disturbing the fixation of at least the modular proximal body portion of the stem. Prior art modular stems include the modular stem as disclosed in U.S. Pat. No. 5,370,706 to Bolesky, et al. and assigned to the applicant of the instant application. The Bolesky patent, U.S. Pat. No. 5,370,706 is hereby incorporated in its entirety by reference.
Another modular stem available in the prior art is the S-ROM® stem sold by DePuy Orthopaedics, Inc., Warsaw, Ind. and described in U.S. Pat. Nos. 4,624,673, 4,790,852, and 4,846,839. The U.S. Pat. Nos. 4,624,673, 4,790,852, and 4,846,839 are incorporated herein by reference in their entireties.
The prior art further includes a modular stem marketed by Wright Medical, Inc. of Arlington, Tenn. The Pro-Femur Stem provides a modular neck with a taper on both ends, one to engage the stem proximal body and one to engage the head.
The present invention is adapted to solve at least some of the aforementioned problems with the prior art.